1. Field of the Invention
The present invention relates to a sheet feed mechanism for feeding sheet materials to a determined position with exact timing and at a high speed, and more particularly to a feed mechanism for feeding image-receiving sheets such as plain paper, insulating paper or chargeable paper in synchronization with a toner image or an electrostatic image formed on an image bearing member such as a photosensitive member or an insulating member, or an original feeding mechanism for feeding sheet originals in succession to an original exposure position.
2. Description of the Prior Art
In recent years, the electrophotographic copiers have been developed toward high-speed duplicators to meet certain market requirements. Such high-speed copying has been confronted technically by mechanical problems resulting high-speed drive of original scanning optical system for high-speed repetitive formation of electrostatic latent image, limitation in copying speed resulting from the photosensitivity of the photosensitive member, increase in power consumption for corona discharge and original illuminating lamp for repetitive latent image formation etc. In order to overcome these difficulties have been developed copiers in which the optical system is fixed, and those in which an electrostatic latent image is repeatedly utilized for image reproduction.
In the following description, the present invention will be explained with reference to the feed mechanism for image receiving sheets for such high-speed copier.
Particularly the above-mentioned copier repeatedly utilizing the latent image is capable of sufficiently elevating the image forming speed since the latent image forming means are utilized only in the first latent image formation and the image reproduction can be conducted regardless of the original scanning speed or the sensitivity of the photosensitive member. Such copier for example utilizes the latent image transfer process or the ion flow modulation process. However, once the high-speed processing in the development step or in the latent image forming step is resolved as explained in the foregoing, there emerges a difficulty in the feeding of image receiving sheets for receiving thus formed images.
The above-mentioned difficulty lies principally in achieving exact positional registration of the image on the image bearing member and the image receiving sheet under high-speed operation. Conventionally such registration is achieved by matching the leading end of the image bearing member with the leading end of the image receiving sheet. More specifically the original image is formed at a reference position on the image bearing member, and the image receiving sheet is advanced so as to meet said reference position. Said advancement is controlled for example by solenoid clutches which are controlled by electric signals from a control unit and which is turn control the sheet feed rollers and registers rollers for final position control. However, in such high-speed apparatus as explained above, the above-mentioned drive system is significantly affected by functional errors resulting from the abrasion of clutches caused by the inertia and repetitive on-off motions of the feed rollers. In addition to the abrasion, the clutches generate heat, thus becoming unable to perform exact functions in response to the input signals and giving rise to aberrared sheet feed timing. Also repeated on-off motions at high speed apply a significant load to clutches unbalanced to the solenoid power, thus shortening the service life thereof.
Also such positional registration is achievable by storing an electric signal indicating the reference position of the original image with respect to the image bearing member in a memory for image-receiving sheet feeding, then activating a control mechanism for a register member by the electric signal from said memory at the start of the sheet feeding, and automatically conducting sheet feeding thereafter mechanically by means of said control mechanism. However, also in such system, the data entry into and data reading from said memory are inevitably associated with certain errors, leading thus to incorrect registration of the image position on the bearing member and the image receiving sheet.